The invention relates to an adaptive active noise control mechanism, and more particularly to a method, active noise control circuit, and portable electronic device for adaptively or dynamically performing active noise control operation upon a target zone such as a quiet zone of a user's ear.
Generally speaking, a conventional active noise cancellation scheme is useful to cancel low frequency noise and now is widely used in earphones for users to have better listening/communication experience. However, it usually generates some high frequency noise which can be heard by users (Hiss noise) in the same time. In order to attenuate Hiss noise, the conventional active noise cancellation scheme may adopt a fixed low-pass filter with a flat frequency response to remove the high frequency part of an anti-noise signal which is used for cancel the Hiss noise. Nevertheless, the fixed LPF with flat frequency response introduces additional latency (side effect) to the conventional active noise cancellation system. The latency inevitably degrades the performance of the conventional active noise cancellation system especially when the system is nearly or completely non-causal. In addition, the fixed low-pass filter with a flat frequency response cannot be used for effectively reduce or cancel different types of noises, and thus side effect is also introduced.